A commonly used design for local area networks is the Ethernet design, particularly as the Ethernet design is set out in the ISO 8802-3 ANSI/IEEE 802.3 standards. The Ethernet design uses the CSMA/CD, or Carrier Sense Multiple Access with Collision Detection methodology to permit multiple stations on the LAN to share access to the media.
Implementations of the Ethernet design typically use a repeater to interconnect media segments. The repeater is a well defined concept; particularly, the IEEE Standard, IEEE 802.3 Section 9.1 to 9.8, sets out a standard design of a repeater employing the CSMA/CD collision detection method.
In one embodiment, a repeater is connected in a star configuration with one station connected to each port of the repeater. In this embodiment there may be as many stations connected to the repeater as there are ports on the repeater.
In an alternative embodiment, a port of the repeater may be connected to a plurality of stations by a shared transmission medium. In this embodiment, each port of the repeater may have a plurality of stations connected thereto, and so the repeater may have many more stations connected to it as there are ports on the repeater.
In either case, each repeater connection represents a LAN segment. LAN segments that are tied together via a repeater experience the same LAN traffic and collision detection and are said to be in the same "collision domain".
In some repeater designs:, there is a provision for a first repeater to be connected to a second repeater. Such a connection is necessary to provide for large networks of stations, particularly where it is desired to join together more stations than one repeater has provision for handling. Such repeater interconnections allow the extension of the collision domain.
An inter-repeater bus, commonly referred to as an IRB, is a method for connecting together two or more repeaters which does not use typical LAN media segments. Repeaters typically plug into the IRB as a module in a chassis arrangement. The repeaters connected to the IRB pass data and state information to and from the IRB. The repeater function, now split across Several modules, operates as specified in the IEEE 802.3 standard.
As networks have grown in complexity, businesses have attempted to centralize network connections in one main area. This area has become known as a communications or wiring closet. Contained in the wiring closet are the electronics to provide the LAN connection functions. These are typically housed in a rack or chassis-like device called a hub or a Smarthub. A hub has a multifuntional backplane that provides mounting, power, and data connection services to the servers, bridges, repeaters, and other network modules often added in a modular fashion. The term Smarthub often refers to hubs containing additional logic or a central processing capability (for manageability), rather than being simply a passive coupling device. Many of the network communications devices are considered stations, and operate above the physical layer of the ISO model.
As is also well known in the art, the number of Ethernet repeater functions (hops) that may be placed in any one communications path between any two stations on the LAN is limited by industry standard configuration rules. It is desired that the distributed repeater function implemented across the IRB count as a single repeater hop between any external media connection.
In addition, repeaters are not the only device which needs access to the LANs on the backplane of the hub. Stations are those devices or portion of other devices (modules) which contain the circuitry and Media Access Control (MAC) capability to be a member of the LAN. With the necessity to add more users and interconnect multiple LANs, other communications devices are added to the Smarthub. These devices might include bridges, and routers, servers and gateways. A method is desired by which to efficiently interconnect these modular devices to each other and to the repeaters.